The present invention relates to steel fiber for reinforcing concrete.
A concrete reinforced by uniformly mixing or scattering short length steel fibers is superior in the tensile strength, bending strength, cracking load, toughness, shock resistance and other properties to unreinforced concrete. Thus, the industrially concerned field has recently paid attention to how to produce the same.
Strengthening characteristics of the steel fiber reinforced concrete depend on properties of the steel fiber to be mixed, and therefore in this regard the steel fiber of the short length excellent in the reinforcing effect has been expected.
Glass fiber or plastic fiber as the short length fiber have been tried, but from viewpoint of various usage or shock-resistability, steel fiber is in general used. There are three kinds of the steel fibers, roughly divided by the production processes as follows.
(a) Steel fiber is cut from wire to the required length. PA1 (b) Slit cold rolled steel sheet whose width corresponds to length of the fiber is chopped by a rotating cutting edge or a pressing mill. PA1 (c) A disc is rotated on molten steel to extract molten steel.
However the steel fibers by the above mentioned processes are not satisfactory. The steel fibers produced by the (a) process of cutting the steel wire and the (b) process of shearing the steel sheet are around (a), square or rectangular (b) in cross section. Since the surfaces are smooth or flat, surface areas are not further widened and therefore it is necessary to increase the amount of the steel fiber mixed into the concrete. The cost charged for the concrete structure becomes high, accordingly. In these circumstances, it is practised to crush the fiber at its both ends or bend it in the center in order to heighten adhesive force to the concrete, but the production steps increase as much and the production cost would become high since much processed raw materials are used. In addition, notwithstanding such additional processings, when mixing into and agitating the fibers in the concrete, the fibers get entangled with each other owing to the crushed or bent portions, thus creating ball-like lumps. The fibers are not uniformly scattered therein. Intentional roughening of the fiber creates cracks and ridges which serve as notches and cause it to be broken thus decreasing the strengthening characteristics. Further since the steel wire material and the steel sheet are used with lubricant during their production, the oil film still remains on the surfaces of the product fibers, which is one of the causes which weaken the adhesion to the concrete matrix.
In the process (c), the fiber is extracted from the molten steel by a water cooled rotating disc. The rotating disc has split spiral screws on its surface, and the molten steel touched at the ridge of the screw is instantly cooled. Thus, the fibers obtained are not uniform in cross section and are lacked in reliability of the adhering property and are inferior in the strengthening characteristics.
In view of such circumstances involved in the prior art, the present invention has as an object to provide improved steel fiber for reinforcing the concrete.
It is an object of the invention to provide steel fiber which is excellent in the strengthening characteristics and the adhering property to the concrete, and may lower the amount necessary to be mixed into the concrete.
It is another object of the invention to provide steel fiber which is well conditioned in dispersion without making fiber balls when mixed into and agitated in the concrete by means of mixer.
It is a further object of the invention to provide steel fiber which may be decreased in the rate of mixing into the concrete and does not need a separator required for using the ordinary steel fibers, and which may lower increasing of the load generated at mixing, thereby to shorten the agitating period of time.
It is a still further object of the invention to provide steel fiber whose surface is covered with oxidized film in blue having an anti-corrosive effect.
It is another object of the invention to provide an improved process which industrially and most effectively produces steel fiber having the above mentioned characteristics at cheap cost.